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Description/Abstract

It has been suggested that people with asthma have a higher prevalence of dysfunctional breathing, lower levels of CO2, and greater sensitivity to CO2 than the general population. Physiotherapists and others base some treatments on such assumptions, but with few data to support them. This study aimed to measure end-tidal CO2 (ETCO2 ) and response to CO2 curves in people with asthma and matched healthy controls. To date 15 people with asthma and 19 healthy controls have been recruited. Baseline data consisted of demographic and anthropometric data; questionnaires on general health, quality of life, asthma control, anxiety and depression, and hyperventilation symptoms; skin prick testing; lung function testing; histamine challenge. ETCO2 levels were measured breath-by-breath using a Rahn-Otis sampler and rapid response CO2 analyser (PowerLab) during 10 minutes of quiet breathing. Response to CO2 curves were generated using a modified Read technique. There is a statistically non-significant difference of .35 kPa in mean ETCO2 measures between the two groups (p=0.08). There is also a statistically non-significant difference (p=0.07) of 4.23 l.min-1.kPa-1 in mean CO2 response slope. Although the difference in ETCO2 has not reached statistical significance it is similar to published data (Osborne et al. 2000 Thorax 55:1016-22) reporting a mean difference of 0.3 kPa in PaCO2 in people with asthma versus non-asthma. The sensitivity to CO2 data do not support the hypothesis that people with asthma are more sensitive to CO2 than the general population.